Blackfin: cm-bf537u: split board from cm-bf537e

The cm-bf537u module, while similar to the cm-bf537e, is different enough
to warrant its own resources.  It has a USB controller but no PHY.

Signed-off-by: Harald Krapfenbauer <Harald.Krapfenbauer@bluetechnix.at>
Signed-off-by: Mike Frysinger <vapier@gentoo.org>